It's only weird if you put Signal's specific design decisions from 2013 on a pedestal and declare it perfect and incapable of being improved.

(N.b. I don't expect my specific suggestions to be adopted. However, I view complaining without offering solutions to be poor form, so I offered some alongside my complaints.)

Of course, any deviation from Signal's design can and should be vetted by the same experts that vetted Signal's. And if they're unavailable to vet the derivations, the conservative thing to do is grit your teeth and bear Signal's legacy until they become available.

However, if Signal still targets Android 4.4 phones in 2020, there's a lot of devices without AES-NI and thus improving upon their AES-CBC design decision is worth probing at least.